This invention relates to the field of optoelectronic devices, and more particularly to resonant reflectors for use with optoelectronic devices.
Various forms of optoelectronic devices have been developed and have found widespread use including, for example, semiconductor lasers, semiconductor photodiodes, semiconductor photo detectors, etc. For some of these applications, an optoelectronic emitter such as a semiconductor laser is coupled to an optoelectronic detector (e.g., photodiode or Resonant Cavity Photo Detector) through a fiber optic link or even free space. This configuration can provide a high-speed communication path, which, for many applications, can be extremely beneficial.
The increased use of all-optical fiber networks as backbones for global communication systems has been based in large part on the extremely wide optical transmission bandwidth provided by optical fiber. This has led to an increased demand for the practical utilization of the optical fiber bandwidth, which can provide, for example, increase communication system user capacity. In the prevailing manner for exploiting optical fiber bandwidth, wavelength-division multiplexing (WDM) and wavelength-division demultiplexing (WDD) techniques are used to enable the simultaneous transmission of multiple independent optical data streams, each at a distinct wavelength, on a single optical fiber, with wavelength-selective WDM and WDD control provided for coupling of the multiple data streams with the optical fiber on a wavelength-specific basis. With this capability, a single optical fiber can be configured to simultaneously transmit several optical data streams, e.g., ten optical data streams, that each might not exceed, say, 10 Gb/s, but that together represent an aggregate optical fiber transmission bandwidth of more than, say, 100 Gb/s.
In order to increase the aggregate transmission bandwidth of an optical fiber, it is generally preferred that the wavelength spacing of simultaneously transmitted optical data streams, or optical data xe2x80x9cchannels,xe2x80x9d be closely packed to accommodate a larger number of channels. In other words, the difference in wavelength between two adjacent channels is preferably minimized. The desire for closely-spaced optical transmission channels results in the need for fine wavelength resolution, which complicates the wavelength-selective WDM and WDD operations required for simultaneous transmission of the channels. Like WDM, Polarization Division Multiplexing (PDM) can also be used to extend the bandwidth of some optical data channels.
The present invention provides an optical system that includes at least two optical emitters and/or optical receivers that have a corresponding guided-mode grating resonant reflector filter (GMGRF). The optical emitters are preferably Vertical Cavity Surface Emitting Lasers (VCSELs), but other optical emitters may be used. Likewise, the optical receivers may be Resonant Cavity Photo Detectors (RCPDs), but other optical receivers may also be used. Each GMGRF is preferably tuned to a unique wavelength and/or polarization by adjusting selected GMGRF parameters, such as the grating period and/or the thickness of the grating or other layers. One advantage of this construction is that the various optical emitters and/or optical receivers may be finely tuned, preferably lithographically, to provide fine wavelength resolution and/or polarization control. For WDM and WDD applications, this may allow for closely spaced optical transmission channels, and may simplify the wavelength-selective WDM and WDD operations required for simultaneous transmission of data channels.
When two or more optical emitters with GMGRF filters are provided, the respective wavelength and/or polarization light outputs may be provided to a common optical element, such as a common optical fiber. Such an optical system may be useful in, for example, WDM, PDM and/or other applications, as desired. In some applications, the various wavelength and/or polarization light outputs may be provided from the optical fiber to the two or more optical receivers, which may then selectively detect a corresponding wavelength and/or polarization. In one embodiment, the optical receivers are Resonant Cavity Photo Detector (RCPD) with a GMGRF incorporated into or adjacent a top mirror thereof. The resonant wavelength of each RCPD is preferably tuned to receive a wavelength and/or polarization of one or more of the optical emitters. This may help simplify the wavelength-selective WDM and WDD operations required for simultaneous transmission of data channels. In another illustrative embodiment, select wavelengths are directed to a particular optical receiver by an optical filter, optical splitter, or the like. In this embodiment, the optical receiver may be a wide band optical receiver, as the wavelength selectivity is provided by the optical filter, optical splitter, or the like, rather than the optical receiver itself. A combination of these embodiments may also be used.
In some embodiments, the GMGRF includes a core layer positioned adjacent a grating layer. The grating layer may extend into the core layer, leaving a core depth between the grating elements and the opposite surface of the core layer. The core layer may have a core thickness, and the grating layer may have a grating period and a grating height. To tune the resonant reflector, and in one illustrative embodiment, the core thickness and grating height may remain substantially fixed, and the grating period may be adjusted or set to produce the desired wavelength. An advantage of this embodiment is that the desired wavelength can be tuned lithographically. In another illustrative embodiment, the ratio of the core depth to the grating height may be set to produce a desired wavelength. In either of these illustrative embodiments, the resonant wavelength of the GMGRF can be tuned to a desired wavelength.
It is also recognized that the wavelength selectivity capability of such GMGRF filters has applicability in display applications. As the grating itself may determine the wavelength of operation, and fabrication is done lithographically, laterally-displaced wavelength dependent emitters can be formed. Such a structure may also serve as a quasi-tunable laser source. Wavelength tunable VCSELs and detectors, as further described below, may also find use in spectroscopic and sensing applications.
The improved performance coupled with the capability to control polarization can also lend itself to applications in polarization-sensitive optical read/write applications. Included are various forms of CD, DVD, and holographic storage applications. Laser printing heads may also benefit. The performance advantage, and use of thinner top and/or bottom mirrors becomes even more paramount when extending VCSELs into the visible wavelengths, where typical all-epitaxial DBRs become prohibitively thick and may require twice as many layers.